/Engine/Source/Runtime/OpenGLDrv/Public/OpenGL.h
Calling glBufferData() to discard-reupload is slower than calling glBufferSubData() on some platforms, because changing glBufferData() with a different size (from before) may incur extra validation. To use glBufferData() discard trick: set to this to true - otherwise, glBufferSubData() will used.
static bool DiscardFrameBufferToResize()